Thermoelectric device having a variable cross-section connecting structure

ABSTRACT

A thermoelectric device having a variable cross-section connecting structure includes a first electrode, a second electrode, and a connecting structure connecting the first electrode and the second electrode. The connecting structure has a first section and a second section. The width of the second section is greater than the width of the first section, and the width of the first section is less than a width that is approximately equivalent to a phonon mean free path through the first section.

BACKGROUND

Thermoelectric devices use the Seebeck effect for generating electricpower from a temperature gradient across the thermoelectric devices.Conversely, thermoelectric devices use the Peltier effect for creating atemperature gradient between the sides of the thermoelectric devicesthrough use of electric power.

The efficiency of a thermoelectric device is measured in terms of ZT,which is the dimensionless figure of merit, defined by,

$\begin{matrix}{{{ZT} = {\frac{S^{2}\sigma}{k}T}},} & {{Equation}\mspace{14mu} (1)}\end{matrix}$

where S is the thermoelectric power, σ is the electrical conductivity, kis the thermal conductivity, and T is the temperature of thethermoelectric device. The thermoelectric power (S), is defined by,

$\begin{matrix}{{S = \frac{\partial V}{\partial T}},} & {{Equation}\mspace{14mu} (2)}\end{matrix}$

where V is the thermoelectric voltage produced per degree temperature(T) difference.

Thermoelectric devices are known to harvest energy that would otherwisebe wasted as heat. The efficiency of thermoelectric devices inharvesting heat energy is generally low.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and not limited in thefollowing figure(s), in which like numerals indicate like elements, inwhich:

FIG. 1 illustrates a cross-sectional side view of a portion of athermoelectric device, according to an embodiment of the invention;

FIG. 2 illustrates a cross-sectional side view of a portion of athermoelectric device, according to another embodiment of the invention;

FIG. 3 illustrates a cross-sectional side view of a portion of athermoelectric device, according to a further embodiment of theinvention;

FIG. 4 illustrates a cross-sectional side view of a thermoelectricdevice, according to a further embodiment of the invention; and

FIG. 5 illustrates a flow diagram of a method of fabricating thethermoelectric devices depicted in FIGS. 1-4, according to an embodimentof the invention.

DETAILED DESCRIPTION

For simplicity and illustrative purposes, the principles of theembodiments are described by referring mainly to examples thereof. Inthe following description, numerous specific details are set forth inorder to provide a thorough understanding of the embodiments. It will beapparent however, to one of ordinary skill in the art, that theembodiments may be practiced without limitation to these specificdetails. In other instances, well known methods and structures are notdescribed in detail so as not to unnecessarily obscure the descriptionof the embodiments.

Disclosed herein is a thermoelectric device that includes at least onen-type section and at least one p-type section. Each n-type section andeach p-type section has a first electrode, a second electrode, and oneor more connecting structures that connect the first electrode and thesecond electrode. The n-type section and the p-type section areconnected in series electrically, but in parallel thermally, such thatthe ends of the thermoelectric device may be at the same temperature.The connecting structure includes at least two sections connected inseries, which are configured to substantially minimize phonon conductionbetween the first electrode and the second electrode while having aproportionately lesser limiting effect on the level of electronconduction through the connecting structure.

With reference first to FIG. 1, there is shown a cross-sectional sideview of a portion 100 of a thermoelectric device, according to anembodiment. The portion 100 shown in FIG. 1 should be understood torepresent one of the n-type region and the p-type region of athermoelectric device, for instance, the thermoelectric device 400 shownin FIG. 4. It should be understood that the portion 100 depicted in FIG.1 may include additional components and that some of the componentsdescribed herein may be removed and/or modified without departing from ascope of a thermoelectric device containing the portion 100. Forinstance, the portion 100 may include additional n-type or p-typeregions of a thermoelectric device as shown in the thermoelectric device400 in FIG. 4.

The portion 100 is configured to either generate electric current from atemperature gradient across the thermoelectric device or to create atemperature gradient across the thermoelectric device throughapplication of an electric current through the thermoelectric device. Asdepicted in FIG. 1, the thermoelectric device 100 includes a firstelectrode 102, a second electrode 104 and a plurality of connectingstructures 110 connecting the first electrode 102 and the secondelectrode 104. Each of the connecting structures 110 includes a firstsection 112 and a second section 114.

The thermoelectric power varies between different materials and, ingeneral, the thermoelectric power for semiconductors is approximately100 times larger than for metals. In addition, the magnitude of thethermoelectric power for a semiconductor depends on the dopingconcentration. The thermoelectric power is typically larger for lowdoped semiconductors and smaller for highly doped semiconductors. In oneregard, therefore, the connecting structures 110 are formed ofsemiconductor material with appropriate doping to produce a sufficientlevel of thermoelectric power.

According to an embodiment, the first section 112 has a width, which isthe dimension that is substantially parallel to the dimension in whichthe first electrode 102 and the second electrode 104 extend, thatsubstantially limits phonon conduction with a proportionately lesserlimiting effect on the level of electron conduction through the firstsection 112. More particularly, the width of the first section 112 issmaller than a width that is approximately equivalent to a mean freepath of phonons and is larger than a width that is approximatelyequivalent to a mean free path of electrons for the one or morematerials forming the first section 112. The mean free path of phononsmay be defined as the average distance covered by the phonons betweencollisions, which is dependent upon the material(s) through which thephonons travel, as well as the temperature of the material(s) at whichthe mean free path of phonons is determined. In addition, the mean freepath of electrons may be defined as the average distance covered by theelectrons between collisions, which is dependent upon the material(s)through which the electrons travel, as well as the temperature of thematerial(s) at which the mean free path of electrons is determined

Generally speaking, the mean free path of electrons is smaller than themean free path of phonons for most materials and at most temperatures.In addition, as the ratio of the width of the first section 112 to thewidth equivalent to the mean free path of phonons decreases, phononscattering increases. Consequently, greatly increased phonon scatteringmay suppress phonon conduction completely or nearly completely, reducingthermal conductivity. Conversely, electrical conductivity, which occursthrough electron or hole carrier movement/mobility in semiconductors,will be substantially less affected as the width of the first section112 is greater than the width equivalent to the mean free path ofelectrons for the material forming the first section 112. The width ofthe first section 112 is thus selected to scatter phonons withoutsubstantially negatively impacting electron or hole carriermovement/mobility through the first section 112.

In conventional thermoelectric devices that are typically comprised ofstructures with larger lateral dimensions, electrical conductivity (σ)tracks thermal conductivity (k). In contrast, the first section 112 isable to partially decouple electrical conductivity (σ) from thermalconductivity (k), because in semiconductors, electrical conductivity isprimarily due to movement of electrons while thermal conductivity isprimarily due to movement of phonons. As the diameter of 112 decreases,the thermal conductivity (k) decreases at a greater rate than electricalconductivity (σ). Consequently, there will be a corresponding increasein efficiency because of the relationship of both to the dimensionlessfigure of merit (ZT). As such, and as discussed above, the first section112 has a width that generally results in the movement of phonons to beminimized while still enabling relatively free movement of electrons.

The first section 112 has a length that is calculated based on distancesthat substantially minimize the amount of electrical resistance in theconnecting structures 110. More particularly, the first section 112 hasa length that may range from a length equivalent to one or a few meanfree paths of phonons for the material forming the first section 112 toa few microns. However, because electrical resistance is directlyproportional to the length of the first section 112, a shorter length ofthe first section 112 is desirable, in order to reduce electricalresistance.

According to an embodiment, the second section 114 has a width that issized to allow phonon and electron conduction through the second section114. More particularly, the second section 114 has a width that may begreater than a width that is equivalent to a mean free path of phononsthrough the material of the second section 114. In one regard, thegreater width of the second section 114 serves to reduce its electricalresistance and thus, the second section 114 may have a width that ismany times larger than the width that is equivalent to a mean free pathof phonons through the material of the second section 114.

In addition, the second section 114 has a length that may be minimizedin order to maximize electrical conduction in the connecting structure110.

By virtue of the first section 112 being in series with the secondsection 114, the total electrical resistance of the connecting structure110 may be greatly reduced when compared to a constant cross-sectionconventional connecting structure of a similar length and a widthsimilar to the first section 112. The connecting structure 110, however,may have a comparable, albeit somewhat lesser, ability to scatterphonons as the constant cross-section conventional connecting structure.

The first section 112 may be formed of, for instance, silicon,germanium, bismuth telluride, lead telluride, bismuth antimonide,lanthanum chalcogenide and the like, including alloys of one or more ofthese materials.

By way of particular example, the first section 112 and the secondsection 114 are comprised of silicon. In silicon, the mean free path forphonons is approximately 100 nm while the mean free path for electronsor holes is approximately 10 nm. As such, in this example, the firstsection 112 has a width that is between 10nm and 100 nm. In addition,the second section 114 has a width that is greater than 100 nm.

By way of a further particular example, each of the connectingstructures 110 has a first section 112 that is comprised of germaniumand a second section 114 that is comprised of silicon with aheterojunction at the interface. The use of multiple materials in thisexample facilitates methods of fabricating the connecting structures 110as described in greater detail herein below.

According to another example, however, the multiple materials may bemade to form an alloy during fabrication of the connecting structures110. In this example, germanium may diffuse at a faster rate intosilicon than silicon diffuses into germanium. Where different materialsare combined into alloys through interdiffusion in the formationprocess, an added benefit is that phonon scattering increasessignificantly in the alloys, in this instance a silicon-germanium alloy.Gradual changes in the composition of the connecting structures 110 maybe achieved by varying the ratio of the multiple materials, such as,precursors, during deposition of the connecting structures 110.Furthermore, the strain induced from the different lattice constants ofthe different materials may also increase phonon scattering.

With reference now to FIG. 2, there is shown a cross-sectional side viewof a portion 200 of a thermoelectric device, according to anotherembodiment. Similar to the portion 100 depicted in FIG. 1, the portion200 shown in FIG. 2 should be understood to represent one of the n-typeregion and the p-type region of a thermoelectric device, for instance,the thermoelectric device 400 depicted in FIG. 4. It should beunderstood that the portion 200 of the thermoelectric device depicted inFIG. 2 may include additional components and that some of the componentsdescribed herein may be removed and/or modified without departing from ascope of a thermoelectric device containing the portion 200.

As depicted in FIG. 2, the portion 200 includes a first electrode 102, asecond electrode 104, and a plurality of connecting structures 210connecting the first electrode 102 and the second electrode 104. Each ofthe connecting structures 210 is comprised of a first section 112, asecond section 114, and a third section 216.

The connecting structures 210 of the portion 200 performs substantiallythe same functions as the connecting structures 110 of the portion 100depicted in FIG. 1. As such, the first section 112 of each of theconnecting structures 210 has a width that is smaller than a width thatis approximately equivalent to a mean free path of phonons and that isgreater than a width that is approximately equivalent to a mean freepath of electrons for the one or more materials forming the firstsection 112. In addition, the second section 114 has a width that isgreater than a width that is approximately equivalent to a mean freepath of phonons for the one or more materials forming the second section114. Similarly to the second section 114, the third section 216 also hasa width that is greater than a width that is approximately equivalent toa mean free path of phonons for the one or more materials forming thethird section 216.

With reference to FIG. 3, there is shown a cross-sectional side view ofa portion 300 of a thermoelectric device, according to a furtherembodiment. Similar to the portion 100 depicted in FIG. 1 and theportion 200 shown in FIG. 2, the portion 300 shown in FIG. 3 should beunderstood to represent one of the n-type region and the p-type regionof a thermoelectric device, for instance, the thermoelectric device 400depicted in FIG. 4. It should be understood that the portion 300 of thethermoelectric device depicted in FIG. 3 may include additionalcomponents and that some of the components described herein may beremoved and/or modified without departing from a scope of athermoelectric device containing the portion 300.

As depicted in FIG. 3, the portion 300 includes a first electrode 102, asecond electrode 104 and a plurality of connecting structures 310connecting the first electrode 102 and the second electrode 104. Each ofthe connecting structures 310 is comprised of a first section 112 and asecond section 314.

The connecting structures 310 perform substantially the same functionsas the connecting structures 110, 200 of the sections 100 and 200depicted in FIGS. 1 and 2. The first section 112 of each of theconnecting structures 310 has a width that is smaller than a width thatis approximately equivalent to a mean free path of phonons and that isgreater than a width that is approximately equivalent to a mean freepath of electrons for the one or more materials forming the firstsection 112. Similarly to the second section 114 depicted in FIGS. 1 and2, a portion of the second section 314 has a width that is greater thana width that is approximately equivalent to a mean free path of phononsfor the one or more materials forming the second section 314. Unlike thesecond sections 114 depicted in FIGS. 1 and 2, however, the secondsection 314 has a tapered shape with a base positioned on the secondelectrode 104 and a top that is connected to and has a similar width tothe first section 112. Although the first section 112 and the secondsection 314 have been depicted as being of the same size at theirintersection location 320, it should be understood that one of the firstsection 112 and the second section 314 may have a larger width than theother one of the first section 112 and the second section 314 withoutdeparting from a scope of the connecting structure 310. In thisinstance, a discontinuity may form at the intersection 320 of the firstsection 112 and the second section 314.

In an alternate embodiment, although not shown, the first section 112also has a tapered shape, similar to the second section 314, with a baseof the tapered shape being in contact with the first electrode 102. Inthis embodiment, the tips of the first section 112 and the secondsection 314 are in contact with each other and at least one of the tipshas a width that is smaller than or approximately equivalent to a meanfree path of phonons and that is greater than a width that isapproximately equivalent to a mean free path of electrons for the one ormore materials forming either or both of the first section 112 and thesecond section 314. In addition, a discontinuity may form at theintersection 320 of the tips of the first section 112 and the secondsection 314. In this instance, one of the tips may have a width that isgreater than a mean free path of phonons for the one or more materialsforming that one of the tips.

With reference to FIG. 4, there is shown a cross-sectional side view ofa thermoelectric device 400, according to an embodiment. It should beunderstood that the thermoelectric device 400 depicted in FIG. 4 mayinclude additional components and that some of the components describedherein may be removed and/or modified without departing from a scope ofthe thermoelectric device 400. For instance, the thermoelectric device400 may include any number of first electrodes, second electrodes, andconnecting structures.

As depicted in FIG. 4, the thermoelectric device 400 includes a firstelectrode 102, a pair of second electrodes 104 and a pair of connectingstructures 410. The first electrode 102 is depicted as being connectedto the second electrodes 104 by a pair of p-type and n-type connectingstructures 410. Although individual ones of the p-type and n-typeconnecting structures 410 have been depicted as connecting the firstelectrode 102 to respective second electrodes 104, it should beunderstood that multiple p-type and n-type connecting structures 410 mayconnect the first electrode 102 to the second electrodes 104.

Although not explicitly depicted in FIG. 4, the connecting structures410 of the thermoelectric device 400 may have the shapes of any of theconnecting structures 110, 210, and 310 depicted in FIGS. 1-3. Inaddition, the thermoelectric device 400 may be provided with amechanical support in addition to the connecting structures 410. Themechanical support may include, for instance, an insulator or a retainedlayer of oxide from a formation process for the thermoelectric device400.

Turning now to FIG. 5, there is shown a flow diagram of a method 500 offabricating the portions 100, 200, and 300 of a thermoelectric device400 depicted in FIGS. 1-4, according to an embodiment. It should beunderstood that the method 500 depicted in FIG. 5 may include additionalsteps and that some of the steps described herein may be removed and/ormodified without departing from a scope of the method 500.

At step 502, at least one first electrode 102 may be provided. By way ofexample, the at least one first electrode 102 may be provided by formingthe at least one first electrode 102 through any suitable process, suchas one or more of growing, chemical vapor deposition, sputtering,evaporating, patterning, bonding, etc. As another example, the at leastone first electrode 102 may be prefabricated and the step of providingmay include positioning the at least one first electrode 102 withrespect to at least one second electrode 104.

At step 504, one or more segments of connecting structure material maybe provided such that as least one of the one or more segments is incontact with the first electrode 102. By way of example, the one or moresegments of connecting structure material are provided by forming theone or more segments of connecting structure material through anysuitable formation process, such as, growing, catalyzed or uncatalyzedchemical vapor deposition, physical vapor deposition, molecular-beamdeposition, molecular-beam epitaxy, laser ablation, sputtering,selective etching, etc. As another example, the one or more segments ofconnecting structure material may be prefabricated and the step ofproviding may include positioning the one or more segments of connectingstructure material such that at least one of the one or more segments ofconnecting structure material is positioned in contact with the firstelectrode 102.

The one or more segments of connecting structure material are comprisedof materials that form the connecting structures 110, 210, 310, 410. Inthis regard, one segment of connecting structure material may compriseone or more materials that form the first section 112, another segmentof connecting structure material may comprise one or more materials thatform the second section 114, 314, etc. In addition, when a plurality ofsegments of connecting structure material are provided at step 504, thesegments may be diffused together to increase phonon scattering asdiscussed above. In any event, the different sections of the connectingstructure 110, 210, 310, 410 may be formed to have the variablecross-sections during formation of the connecting structures 110, 210,310, 410.

Optionally, however, at step 506, the one or more segments of connectingstructure material may be modified if the variable cross sections arenot created during step 504. If performed, the one or more segments ofconnecting structure material may be modified to form one or moreconnecting structures 110, 210, 310, 410 having the respective firstsections 112 and second sections 114, 314 discussed above. The one ormore segments of connecting structure material may be modified throughany suitable process or combination of processes, such as one or moreof, masking, selective etching, oxidation, diffusion, lithography, etc.

By way of a particular example, one or more connecting structures 110,210, 310, 410 may be formed from a plurality of segments of connectingstructure material comprised of different materials. In this example,one of the segments of connecting structure material comprises germaniumand another of the segments of connecting structure material comprisessilicon. The segment of connecting structure material comprising siliconis masked to protect it from ambient oxidation. The segments ofconnecting structure material are then oxidized and germanium dioxide(GeO₂) forms on the segment of connecting structure material comprisinggermanium, which was not masked. The germanium dioxide on the germaniumsegment of connecting structure material may then be selectively removedwithout removing the silicon to form the first section 112, such that,the first section 112 has a width that is smaller than the secondsection 114, 314. In addition, or alternatively, the germanium dioxidemay not be removed from the germanium segment of the connectingstructure material because primary conduction, which includes both heatand electrical conduction, will be through unoxidized regions of theconnecting structures. As such, the germanium dioxide may be selectivelyremoved to obtain desired conduction properties through the connectingstructures. Moreover, the width of the first section 112 formed of thegermanium segment of connecting structure material may be reduced to besmaller than the width that is approximately equivalent to a mean freepath of phonons through the first section 112.

In another example, the segments of the connecting structures are againformed by Ge and Si, and the segments are oxidized. However, in thisexample, the Si segments are not protected by masking. Both the Si andGe segments are oxidized, but at different rates, so that the width ofthe different segments is reduced by different amounts. In a furtherrefinement of this example, the oxidized structure is then exposed to aselective etchant, such as water, that removes Ge oxide, but not Sioxide. The above-described oxidation and etching process is repeated toreduce the diameter of the Ge segments much more than the diameter ofthe Si segments, creating the desired variable cross section of theconnecting sections.

By way of another particular example, one or more of the connectingstructures 110, 210, 310, 410 are formed from a plurality of connectingstructure materials comprised of different materials and the firstsection 112 and the second section 114 are formed through use of thedifferent diffusion rates of the different materials. In this example,one of the segments of connecting structure comprises germanium andanother of the segments of connecting structure comprises silicon.Generally speaking, germanium diffuses faster into silicon than silicondiffuses into germanium. This difference in diffusion rates causes netmass transport from the germanium segment of connecting structure to thesilicon segment of connecting structure, which causes the initialgermanium segment of connecting structure to have a thinner taperedsection as compared with the initial silicon segment of connectingstructure.

At step 508, at least one second electrode 104 may be provided. By wayof example, the at least one second electrode 104 may be provided byforming the at least one second electrode 104 through any suitableprocess, such as one or more of growing, chemical vapor deposition,sputtering, etching, lithography, etc. Alternately, the at least onesecond electrode 104 may be provided prior to formation of theconnecting structures 110, 210, 310, as described in steps 504 and 506.However, providing the at least one second electrode 104 after theconnecting structures 110, 210, 310 are provided may more readilyfacilitate the formation of the thermoelectric devices 100-400 throughprocesses utilizing catalyzed nanowire growth. For instance, pressuremay be varied throughout processes utilizing catalyzed nanowires inorder to vary the diameter of the connecting structures 110, 210, 310.

By way of a further particular example, the method 500 may be used toform a thermoelectric device 400 having connecting structures 410 formedto be n-type and p-type semiconductors as shown in FIG. 4. In thisexample, the thermoelectric device 400 is formed to have a plurality ofconnecting structures 410, in which, the one or more connectingstructures 410 between a particular pair of electrodes 102, 104 aredoped to be either p-type or n-type semiconductors and the one or moreconnecting structures 410 between another particular pair of electrodes102, 104 are doped to be the other of n-type or p-type semiconductors.More particularly, for instance, the p-type connecting structures 410may be masked while the n-type connecting structures 410 are beingprovided and the n-type connecting structures 410 may be masked whilethe p-type connecting structures 410 are being provided to substantiallyprevent cross-contamination between the p-type and the n-type connectingstructures 410.

What has been described and illustrated herein is an embodiment alongwith some of its variations. The terms, descriptions and figures usedherein are set forth by way of illustration only and are not meant aslimitations. Those skilled in the art will recognize that manyvariations are possible within the spirit and scope of the subjectmatter, which is intended to be defined by the following claims—andtheir equivalents—in which all terms are meant in their broadestreasonable sense unless otherwise indicated.

1. A thermoelectric device having a variable cross-section connectingstructure, said thermoelectric device comprising: a first electrode; asecond electrode; and a connecting structure having a first section anda second section, said connecting structure connecting the firstelectrode and the second electrode, wherein the first section has awidth and the second section has a width, wherein the width of thesecond section is greater than the width of the first section, andwherein the width of the first section is less than a width that isapproximately equivalent to a mean free path of phonons through thefirst section.
 2. The thermoelectric device according to claim 1,wherein the connecting structure has a third section, wherein furtherthe first section is located between the second section and the thirdsection, and wherein the third section has a width greater than thewidth of the first section.
 3. The thermoelectric device according toclaim 1, wherein the second section comprises a tapered cross sectionand wherein the first section is connected to a tip at one end of thetapered cross section.
 4. The thermoelectric device according to claim1, wherein the first section comprises a material selected from thegroup consisting of silicon, germanium, bismuth telluride, leadtelluride, bismuth antimonide, lanthanum chalcogenide and alloys of oneor more of silicon, germanium, bismuth telluride, lead telluride,bismuth antimonide, lanthanum chalcogenide.
 5. The thermoelectric deviceaccording to claim 1, wherein the first section comprises a samematerial as the second section.
 6. The thermoelectric device accordingto claim 1, wherein the first section comprises a different materialthan the second section.
 7. The thermoelectric device according to claim1, wherein the first section has a length and the length of the firstsection is greater than a length that is approximately equivalent to amean free path of phonons through the first section.
 8. Thethermoelectric device according to claim 1, wherein the width of thefirst section and the width of the second section form a transitionwherein the transition is untapered.
 9. The thermoelectric deviceaccording to claim 1, wherein the second section has a nanoscale width.10. The thermoelectric device according to claim 1, further comprising:a plurality of second electrodes; a plurality of connecting structures,each of the plurality of connecting structures having a first sectionand a second section, each of the plurality of connecting structuresconnecting the first electrode to the plurality of second electrodes,wherein the width of each of the first sections is less than a widththat is approximately equivalent to a mean free path of phonons throughthe first section, and wherein each of the plurality of connectingstructures is either an n-type or a p-type structure.
 11. Thethermoelectric device according to claim 10, wherein the n-typestructures are arranged in groups and connected between the firstelectrode and a second electrode and the p-type structures are arrangedin groups and connected between the first electrode and another secondelectrode and wherein the groups of n-type structures are alternatelyarranged with the groups of p-type structures with the first electrodeconnecting one end of a group of n-type structures with one end of anadjacent group of p-type structures.
 12. A method of fabricating athermoelectric device, said method comprising: providing a firstelectrode; providing a segment of connecting structure material, whereinthe segment of connecting structure material is connected to the firstelectrode, wherein the connecting structure material has a first sectionand a second section, said connecting structure material is connected tothe first electrode, wherein the first section has a width and thesecond section has a width, wherein the width of the second section isgreater than the width of the first section, and wherein the width ofthe first section is less than a width that is approximately equivalentto a mean free path of phonons through the first section; and providinga second electrode to be contact with the segment of connectingstructure material.
 13. The method according to claim 12, whereinproviding the segment of the connecting structure material furthercomprises utilizing catalyzed nanowire growth processes to grow thesegment.
 14. The method according to claim 13, wherein utilizingcatalyzed nanowire growth process further comprises at least one ofvarying precursors to vary compositions of the segment and varyingpressure applied to the segment to vary diameters of the one or moresegments.
 15. The method according to claim 12, wherein providing thesegment of connecting structure material further comprises causing thefirst section to have a different width as compared with the secondsection through application of oxidation process.